The present invention relates to the manufacture of a porous foam product and an electrode made from the porous foam product. The porous foam product, when filled with an appropriate active material, is useful as a battery electrode.
Reticulated porous products, such as a reticulated polyurethane foam, are generally made in a continuous manner in a block or log form. For example, in U.S. Pat. No. 5,512,222 there is disclosed a method of producing a continuous slab of polymeric foam in which a mixture of liquid foam reactants is introduced into the bottom interior portion of a trough with an open top. The foam mixture then expands upwardly in the trough.
The blocks, often shaped somewhat like a loaf of bread, are then xe2x80x9cpeeledxe2x80x9d around a core, which is oriented along a major axis of the foam, typically the x axis, i.e., the width of the block, or around the y axis, i.e., the length of the block. This method permits the largest flexibility for peeling long continuous strips in maximum width while minimizing waste. Peeling in this manner produces a foam with pores whose aspect ratio varies in a periodic manner from round to oval.
This produces a product with physical properties that vary in the longitudinal direction, i.e., y-axis direction.
There is still a need for continuously and efficiently producing a sponge-like porous article in strip form which can be utilized, for example, in preparing high density, high capacity battery electrodes. It would be desirable to prepare such articles not only having the desired electrical properties, but also tailored to achieve enhanced mechanical properties.
The present invention pertains to making porous products including metal foams that can serve as the matrix material for battery electrodes having high current density, high capacity characteristics. The porous products, typically in the form of metal foam sheets, can further have enhanced tensile strength and elongation, and lower resistivity. They furthermore exhibit lower longitudinal weight variation. When filled and serving as battery electrodes, the articles can exhibit higher battery capacity, decreased variation in cell capacity, and higher voltages during high drain rates.
In one aspect, the invention is directed to the method of producing a three-dimensional reticulated sheet of polymeric foam from a prepared first mass of polymeric foam, wherein the prepared first mass of polymeric foam has a y axis length, an x axis width, and a z axis height, and the polymeric foam sheet can be produced from the prepared first mass by peeling the sheet from the first mass in a plane at least substantially parallel to the y axis length, the improvement in the method of producing polymeric foam sheet comprising the steps of:
establishing a second mass of foam from the prepared first mass of polymeric foam, the foam second mass retaining the x, y and z axes of the prepared first mass;
shaping the foam second mass for peeling the foam in a plane at least substantially parallel to the z axis; and
peeling a sheet of polymeric foam, from the shaped foam second mass in a plane at least substantially parallel to the z axis.
In another aspect, the invention is directed to a method of producing an electrode for a battery, comprising the steps of:
providing a foam support member, with the support member having a multitude of pores;
establishing the foam support member in sheet form, having a sheet length in the longitudinal direction and a sheet width in the transverse direction, with the pores having a uniform pore aspect ratio in the longitudinal direction;
coating the foam support member with an electroconductive coating; and
introducing active material into the sheet form electrode support member to produce an electrode in sheet form containing the material in the sheet.
In yet another aspect, the invention is directed to an apparatus for preparing a three-dimensional reticulated sheet of polymeric foam from a prepared first mass of polymeric foam, wherein the prepared first mass of polymeric foam has a y axis length, an x axis width, and a z axis height, and the polymeric foam sheet can be produced from the prepared first mass by peeling the sheet from the first mass in a plane at least substantially parallel to the z axis, which apparatus comprises:
foam supply production means producing a polymeric foam mass having a y axis longitudinal direction; and
cutting means severing the foam supply into sheet form having a length along the z axis of the foam mass.
In a still further aspect, the invention is directed to a porous foam article, which article is a three-dimensional reticulated foam article having a substantially cylindrical outer surface, and having an x-axis radius, a y-axis radius and a z-axis height, wherein the outer surface is cylindrical around the z-axis, the article consisting of a multitude of pores, the article providing a uniform pore aspect ratio in the longitudinal direction for a sheet of foam severed from the article, wherein the sheet has longitudinal direction in the x-axis direction.